diff --git a/actionpack/lib/action_dispatch/routing/mapper.rb b/actionpack/lib/action_dispatch/routing/mapper.rb
index f4d31eeff1..fb1f0d3f0c 100644
--- a/actionpack/lib/action_dispatch/routing/mapper.rb
+++ b/actionpack/lib/action_dispatch/routing/mapper.rb
@@ -968,6 +968,21 @@ def resource(*resources, &block)
         #   PUT     /photos/:id
         #   DELETE  /photos/:id
         #
+        # Resources can also be nested infinitely by using this block syntax:
+        #
+        #   resources :photos do
+        #     resources :comments
+        #   end
+        #
+        # This generates the following comments routes:
+        #
+        #   GET     /photos/:id/comments/new
+        #   POST    /photos/:id/comments
+        #   GET     /photos/:id/comments/:id
+        #   GET     /photos/:id/comments/:id/edit
+        #   PUT     /photos/:id/comments/:id
+        #   DELETE  /photos/:id/comments/:id
+        #
         # === Supported options
         # [:path_names]
         #   Allows you to change the paths of the seven default actions.